Terfenadine. Is it unsafe?
The Committee on Safety of Medicines in the UK has decided that this widely used antihistamine should be available on prescription only, and not by direct purchase from pharmacists. The reason is that deaths have occurred from its use when it has been taken together with some other drugs or in people with a particular group of heart problems.
Should you stop taking terfenadine? And what is the best alternative?
Table of Contents
- Is my medicine Terfenadine?
- What is Terfenadine?
- What is the problem with Terfenadine?
- How would I know if this was happening to me?
- Do any other antihistamines cause the same problem?
- What are the alternative medicines?
- Hair loss; an occasional mild side effect?
- Conclusion
In Britain, terfenadine is available only on prescription by a doctor. Until recently it was available without prescription, but this has been stopped because of the safety problem. It has been sold under many names, for example:
Is my medicine Terfenadine?
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What is Terfenadine?
Antihistamines help against allergies by blocking the action of histamine, a chemical released in the body during allergic reactions. Histamine causes itching, redness (by making blood vessels wider), swelling (by making blood vessels leaky), narrowing of the air tubes in our lungs (by making the muscle around the tubes contract and also by swelling and by causing increased mucus formation) and other effects which are part of allergic reactions.
The antihistamines we had before terfenadine are still used by many people. These older antihistamines may make you sleepy. But even if they don't, they make you a worse driver and interfere with mental function. Terfenadine was the first of the newer antihistamines which don't have these disadvantages.
It is possible that the older antihistamines which are still widely used cause road accidents. At the moment we do know that this is likely to be true, but we don't have direct proof that actual individual deaths on the road are caused by older antihistamines.
Terfenadine was the most widely used of the newer antihistamines which don't cause a lot of drowsiness and sedation until recent years, when other antihistamines overtook it. The reason for its decline was that on rare occasions it caused deaths due to interactions with other medicines and medical conditions.
The successor to terfenadine, called fexofenadine does not have this safety problem. You can get fexofenadine on prescription but not yet without prescription..
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What is the problem with Terfenadine?
- Ketoconazole
- Itroconazole
Though the following combinations must have been taken by huge numbers of people without any known side effects, it is thought that a similar risk might exist if terfenadine is taken with:
- Erythromycin
- Grapefruit juice (but not orange juice or fresh grapefruit)
In these larger amounts, terfenadine slows down the 'recharging of the batteries' in the heart muscle after each heartbeat. If this recharging becomes too slow, a dangerous or even fatal abnormal heart rhythm results.
For the same reason, terfenadine is dangerous in:
- People who take other medicines for heart disease which delay the recharging of the heart muscle 'batteries'
- People who have a rare similar abnormality of the heart muscle before they take terfenadine
For these reasons treatment with terfenadine should be supervised by a doctor. The new medicine fexofenadine does not have this problem, but is not available without prescription. This is because the Committee on Safety of Medicines normally demands that a medicine should have been available on prescription from doctors for 18 months before it will allow it to be sold without prescription.
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How would I know if this was happening to me?
The warning which people have had has consisted of spells of faintness. An electrical tracing of the heart, or ECG (electrocardiogram), can tell immediately if your heart is being affected in this way.
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Do any other antihistamines cause the same problem?
As medicines go, this antihistamine still rates as a rather safe treatment. The same is true for terfenadine. With both, the hazard is very low indeed if the instructions are followed. No medicine is completely safe.
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What are the alternative medicines?
The following is a table of the alternatives:
| Official name | Trade names | Comment |
| acrivastine | Semprex | Three times daily dosage in its UK form makes it less popular for hay fever |
| cetirizine | Zirtec | Once daily May not be so free from sedative effect as the others |
| fexofenadine | Telfast 120 (UK), Allegra (USA) | Once daily The successor to terfenadine |
| loratadine | Clarityn | Once daily |
| mizolastine | Mizollen | New. Claimed to have high effectiveness. |
All these medicines are safer than old-fashioned antihistamines which cause sleepiness or impaired performance in driving, learning and other tasks.
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Hair loss; an occasional mild side effect?
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Conclusion
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Its last update was on 28 Mar 2000
Copyright © 1998 M. A. Stern